Catalysts of various sorts, specifically heterogeneous catalysts, usually have a shortcoming: they are difficult to handle. Techniques to modify these catalysts so that they are more easily handled are limited. For example, agglomeration with "binders" is unsuitable since "binders" normally poison the catalyst sites.
Techniques such as sieving the heterogeneous catalysts to remove the catalyst "fines" is a possible technique; however, it is a technique that is expensive. Furthermore, a catalyst manufacturer must then have an outlet for the catalyst "fines" which he accumulates.
Certain heterogeneous catalysts may be sintered with a binder with concomitant loss of catalyst sites. The sintered material may then be extruded or fractured to yield a large heterogeneous catalyst. The problem with this procedure is that it is not applicable to all heterogeneous catalysts, and in some cases damages the catalyst.
With certain catalysts such as olefin polymerization catalysts, the growth of the catalyst itself from the original catalyst seeds can be controlled to yield products having a coarse structure (20 microns or larger) which makes these catalysts more easily handled. Thus, A. P. Haag and M. Weiner (U.S. Pat. Nos. 3,623,846, issued Nov. 30, 1971, assigned to Dart Industries, Inc.) described a process for controlling particle size during condensation and/or desublimation of a material such as titanium trichloride which may be used in the polymerization of alpha-olefins.
In another example as described in British Pat. No. 1,139,450, assigned to Shell Internationale Research Maatschappij, TiCl.sub.3 catalysts are formed by controlled reduction of titanium tetrachloride with aluminum alkyls. These materials have a narrow particle size distribution, and have an average diameter greater than 15 microns, and therefore are relatively easy to handle.
However, the latter two examples illustrating two techniques for improving the particle size of catalysts, specifically titanium trichloride olefin polymerization catalysts, have certain limitations. Thus, although the catalyst particle size is greater than the 1 micron dimension which is normally available, the 20 micron size still limits the useability of these catalysts. Increase in catalyst growth to yield particles 100 microns or larger is more difficult. Furthermore, control of particle size during catalyst synthesis is a problem unique to every type of catalyst that might be employed. What is desired, therefore, is a technique that is applicable to heterogeneous catalysts in general, a procedure that is easy to employ, and one that can yield catalysts in shapes and sizes most suitable to each process in which the catalyst is to be used.
In U.S. Pat. No. 3,990,993 (assigned to Exxon Research and Engineering Company) a procedure is described whereby olefin polymerization catalysts, i.e. Ziegler TiCl.sub.3 -nAlCl.sub.3, can be mechanically treated with a fibrillatable polytetrafluoroethylene (PTFE) in order to trap the catalyst "fines" in a web of PTFE microscopic febers, thus producing a catalyst of larger particle size having a more narrow particle-size distribution. Nevertheless, the catalyst is still limited in size obtainable and in particle size distribution by the randomizing technique of fracturing the catalyst-PTFE mixture.
Further, as an expression of the prior art, U.S. Pat. No. 3,051,662 (assigned to Phillips Petroleum Company) describes the use of polyolefins as binders and lubricants for shaping solid materials. The disclosure teaches the formation of simple mixtures which are extruded through a die. In some instances where metal oxide catalysts are involved, the lubricant-binder of the invention is removed, usually by incineration or vaporization. This would destroy the activity of many catalysts. PTFE is only casually mentioned, and the disclosure fails completely to recognize the importance of the invention as disclosed and claimed herein. While it is pointed out that the patentee is concerned with the particle size range of various catalytic materials and the desirability to form these materials into large, uniform, easily handled shapes, U.S. Pat. No. 3,990,993 clearly expresses concern for fines resulting from ballmilling of polyolefin catalysts. Such concern is unnecessary in the practice of this invention.
Further, U.S. Pat. Nos. 3,838,062, 3,838,092, and 3,993,584 disclose the use of a fibrillatable PTFE to create a weak agglomerate of dusts, particularly toxic dusts.